Projectiles that are launched at a target are generally equipped with a guidance system to accurately intercept the target in required time. When equipped with a GPS receiver, a guidance system can use current projectile position as measured by the GPS along with known target location derive flight corrections required to intercept the target. The guidance system also requires knowledge of the attitude of the projectile in flight at each moment in order to accurately intercept the target in the required time. The term, ‘attitude’ of the projectile in flight as used herein above and below may refer to a roll attitude, a pitch attitude, and a yaw attitude of the projectile in flight. Further, the GPS guidance system based on the attitude of the projectile precisely determines corrections, such as acceleration corrections, required by the projectile in flight for accurately intercepting the target.
To implement the required corrections, the GPS guidance system of the projectile needs to have knowledge of the roll attitude of the projectile in flight. Additionally, the projectile while in flight using a proportional navigation (a guidance technique) requires corrections for gravity. For the corrections of gravity, knowledge of the roll attitude and the pitch attitude of the projectile is also required.
Various approaches for determining the roll attitude of the projectile involve sensing of a GPS signal by the GPS guidance system of the projectile while the projectile spins. Further, the sensed GPS signal may be combined with the known information about location of a satellite communicably coupled to the projectile for providing a low bandwidth measurement of the roll attitude of the projectile in flight. However, the low bandwidth measurement of the roll attitude of the projectile in flight is sensitive to a roll rate, and accordingly, determination of a down angle of the projectile may not be made as the roll rate approaches to zero value. Furthermore, the combined information of the sensed GPS signal and the known information about the location of the satellite may not be used to determine the pitch attitude and the yaw attitude of the projectile in flight.
Other approaches for determining the attitude of the projectile in flight include sensing the rate of change of the pitch attitude (for example, an angular rate) using a gyroscope. In this approach, an arctangent of the sensed rate in a projectile pitch axis and the projectile yaw axis provides a direct measurement of the roll attitude. However, such an approach is corrupted by any coning motion (gyroscopic precession) of the projectile and/or guidance corrections that impart pitch rate and yaw rate disturbances. Furthermore, the aforementioned approach is influenced by bias and noise in the direct measurement carried out by the gyroscope.
Accordingly, there is a need for an efficient and effective system and a method for determination of attitude for a projectile in flight, in a manner wherein the determination of attitude for a projectile in flight is insensitive to roll rate, day/night operation and maneuvers.